pyperformance run creates its venv relative to the current directory

pyperformance run --python=X puts the benchmark venv in ./venv/<python-id>-compat-<hash> under the current working directory, not next to the pyperformance install. Launched from another directory (for example a backgrounded cd dir && a & b &, where the cd applies only to the first command), it builds a fresh venv, losing any .pth or packages you added, or fails at once with VenvCreationFailedError if the cwd is read-only. In a driver script, cd to a fixed directory first, or pass --venv explicitly.